The invention is based on a fuel injection system for internal combustion engines.
One such fuel injection system is known from the literature, for instance from the textbook Dieselmotor-Management [Diesel Engine Management], 2nd Edition, Verlag Vieweg, page 299. For each cylinder of the engine, this fuel injection system has one fuel pump, one fuel injection valve, and one line connecting the fuel injection valve to the fuel pump. An electrically controlled control valve is disposed on the fuel pump and by the control valve a communication of the high-pressure side of the fuel pump with a relief chamber is controlled. In a known manner, the fuel injection valve has an injection valve member, by which at least one injection opening is controlled, and which has a pressure shoulder defining a pressure chamber; the pressure chamber communicates with the line, and the injection valve member can be lifted from a valve seat, counter to a closing force for opening the at least one injection opening, by fuel under high pressure delivered to the pressure chamber by the fuel pump. By means of the control valve, the time and duration of opening of the fuel injection valve can be controlled; the time of opening is determined by the disconnection of the high-pressure side of the fuel pump from the relief chamber by the control valve, and thus the high pressure generated by the fuel pump acts at the fuel injection valve. For closing the fuel injection valve, the communication of the high-pressure side of the fuel pump with the relief chamber is opened by the control valve, so that high pressure that would open the fuel injection valve is no longer operative in the fuel injection valve. The control valve is disconnected by the line and is located relatively far away from the fuel injection valve, so that when the communication of the high-pressure side of the fuel pump with the relief chamber is opened, the pressure in the pressure chamber of the fuel injection valve drops only in delayed fashion, and the fuel injection valve correspondingly closes only with a delay, so that the closing time and thus the duration of opening of the fuel injection valve can be determined only imprecisely. A brief opening of the fuel injection valve for a preinjection is likewise feasible only with difficulty, because of the delayed pressure change at the fuel injection valve. Varying the course of the opening stroke of the injection valve member of the fuel injection valve, in order to attain a certain course of the quantity of injected fuel during the opening duration of the fuel injection valve, is likewise feasible only with difficulty in the known fuel injection system.
The fuel injection system according to the invention has the advantage over the prior art that fast closure of the fuel injection valve without any delay is assured by the second control valve. Also by the second control valve, a brief opening duration of the fuel injection valve is attainable, as is required for a preinjection, for instance. Furthermore, the opening stroke of the injection valve member can be varied by means of the second control valve.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawing.